JPH0781701B2 - A device for estimating unburned content in ash of a coal combustion furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention monitors the concentration of unburned ash in ash contained in the combustion exhaust gas of a coal combustion furnace to efficiently operate the combustion furnace. Estimator

[0002]

2. Description of the Related Art Recently, coal has been reviewed as an alternative energy to oil, and pulverized coal combustion technology has attracted attention as a boiler for power generation. This technology itself has already been completed, and the coal is pulverized by a pulverized coal machine (mill), the obtained coal powder is separated into coarse coal and pulverized coal by a coarse powder separator, and only the pulverized coal is gas from the burner. It is something that is jetted out and burned like.

FIG. 4 shows a schematic diagram of a power generation boiler using a pulverized coal combustion system. In the figure, the coal stored in the coal feeder 10 is sent to a mill 11, crushed by a roller 12 to a required particle size, and separated by a coarse powder separator 13 into coarse coal and fine coal. The coarse powder separator 13 includes a vane system that separates the coarse coal and the fine coal by changing the opening of the blade (vane) and a rotating system that separates the coarse coal by centrifugal separation.

The pulverized coal separated by the coarse powder separator 13 is sent to the burner 15 of the combustion furnace 14 together with the primary air. The primary air is air for transporting the pulverized coal to the burner 15 at the same time as drying the coal to facilitate combustion, and about 10 to 30% of the amount of air required for combustion is used. The remaining air is provided as secondary air from around the injection port of the burner 15. In addition, tertiary air may be supplied to stabilize ignition or adjust the shape of the flame. Further, apart from the burner 15, the two-stage combustion air by the two-stage combustion method is given from an appropriate part of the combustion furnace 14 in the traveling direction of the combustion gas. Each of these air is sent from the forced draft fan 16 through the air preheater 17. The amount of the two-stage combustion air is adjusted by the two-stage combustion air damper 18.

The heat generated in the combustion furnace 14 is transferred to the water in the evaporated water pipe 19 by radiation or contact of combustion gas,
Evaporate the water. Combustion gas passes through an air preheater 17 for recovering heat and is discharged from a chimney 21 by an induced draft fan 20.

When operating the boiler, nitrogen oxides (NOx) and sulfur oxides (SOx) contained in the combustion gas are used.
In addition to suppressing harmful substances such as
It is necessary to reduce unburned components (H ₂ , CH _4, etc.) in ash that affect combustion efficiency. Especially in the case of a coal-fired boiler, the combustion speed is much slower than that of fuels such as oil and gas, so the temperature of the combustion furnace decreases and the two-stage combustion method, which is a low NOx combustion method, is used. Since the temperature of 1 decreases, the residual amount of unburned matter in ash tends to increase.

The unburned content in the ash varies greatly depending on the particle size of the coal burned in the burner 15. The finer the particle size of the fine powder, the larger the surface area that comes into contact with the combustion air, so that it burns well and reduces the unburned content in ash. Therefore, while the boiler is operating, the concentration of unburned ash in the exhaust gas is monitored, and when the concentration of unburned ash is increased, the coarse powder separator 13 is controlled to reduce the fine powder particle size and burn it. We need to increase efficiency.

[0008]

By the way, in pulverized coal combustion, many factors such as fuel ratio, ash content in coal, and particle size distribution are complicatedly involved. Therefore, it is necessary to estimate unburned ash content in the combustion process. Is extremely difficult. Therefore, a peep window is provided on the furnace wall of the combustion furnace, the combustion flame of the burner is photographed from this window, the flame temperature is calculated from the obtained flame image, and the flame temperature, coal supply amount, air supply amount, preheat A technique has been proposed in which a combustion rate is obtained from data such as air temperature, and the concentration of unburned matter in ash is estimated from this combustion rate and ash content in coal (for example, see Japanese Patent Laid-Open No. 208412/1990). ).

However, according to this conventional technique, a camera is installed on the wall of the combustion furnace, an analog video signal taken by this camera is converted into a digital video signal, and the flame temperature is calculated from the flame image by the digital image processing technique. Therefore, the apparatus becomes complicated, and in addition to the flame temperature, the temperature distribution and the air ratio distribution along the combustion process are required to calculate the unburned ash content at the outlet of the combustion furnace. It is difficult to measure the temperature distribution and air ratio distribution for the entire combustion furnace when targeting a practical furnace.

The present invention is capable of inferring the concentration of unburnt ash content in flue gas, which has an influence on combustion efficiency, from the current situation by a simple means, and obtains the unburnt ash content in coal combustion furnaces. It is an object to provide an estimation device.

[0011]

DISCLOSURE OF THE INVENTION The present invention relates to a pulverized coal combustion type coal combustion furnace, including the temperature inside the combustion furnace, the load zone of the combustion furnace, the dirt coefficient of the combustion furnace, and the two-stage combustion air supplied to the combustion furnace. And the mixed coal ratio of the coal supplied to the combustion furnace as fuzzy quantities, and corrects the standard values of the standard furnace temperature distribution, standard furnace air ratio distribution, and standard pulverized coal particle size distribution that have been obtained in advance. Data and fuel ratio data are inferred, and the unburned ash concentration in the flue gas is calculated based on each reference value after being corrected by this correction data and the reaction rate ratio data of the coal obtained from the fuel ratio data. It is characterized by

[0012]

In the ash unburnt content estimating apparatus according to the present invention, the temperature in the combustion furnace, the load zone of the combustion furnace, the dirt factor of the combustion furnace, the proportion of the two-stage combustion air supplied to the combustion furnace, and the supply to the combustion furnace. Each data of coal mixing ratio of coal is evaluated qualitatively by the corresponding membership function as a fuzzy amount, and it is the value evaluated from the predetermined fuzzy rule how to set the output in a certain situation. Retrieval of rules and fuzzy inference are used to infer correction data and fuel ratio data for correcting reference values of reference in-reactor temperature distribution, reference in-reactor air ratio distribution and reference pulverized coal particle size distribution.

Based on the correction data thus inferred,
The reaction rate of coal was corrected theoretically or experimentally in advance by correcting each reference value of the temperature distribution in the standard furnace, the air ratio distribution in the standard furnace, and the standard pulverized coal particle size distribution. Calculate ratio data. Then, the unburned ash concentration is calculated based on the corrected reference values and the reaction rate ratio data.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the apparatus for estimating the unburned matter in ash of a coal combustion furnace according to the present invention. This device sequentially takes in each data such as temperature TM in the combustion furnace, load signal QS, in-furnace fouling coefficient ζB, two-stage combustion air ratio TS, mixed coal ratio MC, etc. A fuzzy inference unit 1 which infers the correction values of the ratio of the air amount to the actual air amount) λ, the pulverized coal particle diameter Dp, and the carbonaceous fuel ratio (ratio between the volatile component and the fixed carbon component) FR, and theoretically in advance. Or the reference part 2 in which the distribution of the in-reactor temperature T, the distribution of the in-reactor air ratio λ, the distribution of the particle diameter Dp, and the distribution of the reaction rate ratio β depending on the carbonaceous substance, which are experimentally obtained, are prepared as reference distribution models. And a correction unit 3 for correcting the reference values of the furnace temperature T, the furnace air ratio λ, and the pulverized coal particle diameter Dp obtained from the reference unit 2 based on the corresponding correction values obtained from the fuzzy inference unit 1. , Each value T corrected by the correction unit 3,
The calculation unit 4 calculates the unburned ash content C based on λ, Dp and the reaction speed ratio β output from the reference unit 2.

The fuzzy inference unit 1 is, as shown in FIG.
The evaluation unit 1a, the rule unit 1b, and the inference unit 1c are included. The evaluation unit 1a includes furnace temperature data TM measured by a temperature sensor installed in the combustion furnace 14 and two-stage combustion air damper 1
Two-stage combustion air ratio data TS obtained from the manipulated variable of 8,
Each data such as the coal mixing ratio MC of the coal supplied to the mill 11 is taken in as a fuzzy amount, and each of these data is qualitatively evaluated by the corresponding membership function.
The rule part 1b describes and stores the rule of how to set the output in a certain situation in the form of "if antecedent part then consequent part" based on the abundant database accumulated so far. . The inference unit 1c searches the rule unit 1b for a rule that matches the value evaluated by the evaluation unit 1a, and corrects the correction value T'of the reference furnace temperature distribution T, the correction value λ'of the reference furnace air ratio distribution λ, and the reference particles. The respective correction values of the correction value Dp 'of the diameter distribution Dp and the fuel ratio FR are respectively inferred.

Now, the temperature data TM in the furnace is m1,
The rule regarding the temperature inside the furnace is “if TM = sm then
"T '= sm" (rule 1), "if TM = md then"
T ′ = md ”(rule 2),“ if TM = bg then
If there are three rules of “T ′ = bg” (rule 3), the degree (ambiguity) f1 and f that applies to this rule from the membership function regarding the temperature in the furnace of the evaluation unit 1a.
2 is obtained.

In the inference unit 1c, "max-
min logical product ”is applied, and the degree f1 is calculated based on rule 1.
Flat membership function and the consequent "T '= s
AND with the membership function of "m", and similarly, based on rule 2, the AND of the flat membership function of the degree f2 and the membership function of "T '= md" in the consequent part is obtained. . Schematically, as shown in FIG. 3, the membership function of each consequent part is truncated, and s
Determine m '(figure a) and md' (figure b). Then
The center of gravity of the figure is obtained by the center of gravity method by taking the logical sum of sm 'and md' (Fig. c), and the value q of the base set of the obtained center of gravity is obtained.
1 is the definite output T '(correction value of furnace temperature T). The other outputs λ ′, Dp ′, FR are similarly obtained. The fuzzy labels “sm”, “md”, and “bg” in the figure are “correction amount small (small)” and “correction amount medium (middl), respectively.
e) ”and“ large correction amount (big) ”.

The reference section 2 is a reference temperature distribution table 2a showing the distribution of the in-furnace temperature T with respect to the furnace length DL of the combustion furnace,
Reference air ratio distribution table 2b showing distribution of in-reactor air ratio λ with respect to furnace length DL, reference particle size distribution table 2c showing distribution of coal particle size Dp, and reaction of coal with fuel ratio FR inferred by fuzzy inference unit 1 It has a reference reaction speed ratio distribution table 2d showing the distribution of the speed ratio β. The data stored in each of these tables is theoretically or experimentally obtained in advance. The furnace length DL of the combustion furnace is supplied from the arithmetic control unit 4e.

The correction unit 3 includes the tables 2a to 2 of the reference unit 2.
In-furnace temperature T output from c, in-furnace air ratio λ, particle size D
The reference data of p is corrected based on the corresponding correction values T ′, λ ′, Dp ′ inferred by the fuzzy inference unit 1, and each corrected data is supplied to the arithmetic unit 4. It is easy to adjust the correction that makes use of the features of "if ~ then
A rule expression of the form "~" is possible, and the ambiguity of measurement signals can be considered in the rule expression. The correction calculation is performed by adding and subtracting the temperature distribution in the furnace with consideration of the deviation of the temperature distribution from the load zone and the fouling coefficient, and the furnace air ratio and particle size distribution are calculated in the form of products.

The calculation unit 4 calculates the diffusion rate K _MT of oxygen when the diffusion rate is controlled (infinite chemical reaction) based on the data supplied from the reference unit 2 and the correction unit 3. Based on the reaction rate-controlling rate calculation unit 4b that calculates the surface reaction rate K _CH when the surface reaction rate is controlled (infinite diffusion rate), the unburned rate calculation unit 4c that calculates the unburned rate u of pulverized coal, and the unburned rate u An ash unburned-content calculating unit 4d for calculating the ash unburned-content concentration C, and a calculation control unit 4e for controlling each of these calculating units.

Generally, the combustion process of pulverized coal particles blown into the combustion furnace is divided into two stages, that is, gas combustion of volatile components and surface combustion of the remaining solid particle portion (char), and most of the combustion time is It is occupied by char burning in the second half. The overall burning rate of char is determined by the diffusion rate of oxygen to the particle surface and the chemical reaction rate on the particle surface.The former depends on the mixing characteristics of fuel and air, and the latter depends on the chemical properties of fuel, but Physical properties such as the particle size of charcoal and its movement are also relevant.

According to Kurata et al., The overall burning velocity "dm / dt" of char is dm / dt = -πDp ² × 1 / (1 / K _MT + 1 / K _CH ) ... m: particle mass Dp: particle diameter K _MT : oxygen diffusion rate K _CH : surface reaction rate.

The diffusion rate K _MT is calculated by the diffusion rate controlling rate calculation unit 4a, and the surface reaction rate K _CH is calculated by the reaction rate controlling rate calculation unit 4b. The diffusion rate K _MT is

[Equation 1] D: oxygen diffusion coefficient ρ: gas density Dp: particle size T: furnace temperature γ: value determined by diffusion coefficient and stoichiometric coefficient of combustion reaction (γ≈-1) fm: expressed by oxygen mass fraction . The subscript "0" represents the standard state.

The reaction rate K _CH is expressed by K _CH = K _CH '× β = K _CH ' {1+ (2 / FR) ^1.5 × 2} / 3, where β is the above reaction rate ratio and FR is the above. Is the combustion ratio. K _CH 'represents the average surface reaction rate of a wide range of coal, which varies depending on the carbon quality, and is therefore corrected by the reaction rate ratio β determined from the fuel ratio FR representing the carbon quality. The average reaction rate K _CH 'is K _CH ' = 8710 exp (-17980 / T) x Po (T ≤ 1500 K) = (3.85 x 10 ^-4 T-0.525) x Po (T> 1500 K). Po: Expressed by oxygen partial pressure (atm).

[0025] The relationship between the oxygen partial pressure Po and the reference air ratio distribution λ _{is, Po / Ptotal = Vo 2 /} Vtotal = O 2% Ptotal: total pressure (atm) Vo _2: Oxygen volume Vtotal: total volume O ₂ %: Oxygen concentration (%) From λ = 21 / (21-O ₂ %), Po = Ptotal × 21 (λ-1) / λ.

Next, the unburned rate calculator 4c calculates the unburned rate u based on the diffusion rate K _MT and the reaction rate K _CH thus obtained. The decrement of the mass due to combustion is obtained by integrating the overall combustion speed (formula) of char with the combustion time. Therefore, the unburned rate u after the burning time S of the carbon content per unit mass is obtained from the following equation.

[Equation 2]

Therefore, assuming that the ash content of the raw coal is A, the unburned carbon content per unit mass is "u (1-A)".

[Equation 3] Becomes The ash ratio A is the composition of coal including fixed carbon, volatile matter,
It is the proportion of ash in the water and ash divided into four and expressed as a weight percentage.

Based on the concentration C of the unburned matter in the ash thus obtained, the vane opening or the rotation speed of the coarse powder separator 13 is controlled, and the particle size of the pulverized coal is adjusted. The concentration of can be led to the stable region. In the above-described embodiment, the "max-min logical product" is applied as the inference method, but the invention is not limited to this, and other inference methods such as "max-min algebraic product" may be applied. May be.

[0029]

According to the present invention, the concentration of unburned ash contained in combustion exhaust gas can be qualitatively obtained by a simple means with a simple means by fuzzy reasoning, and an efficient coal combustion furnace can be obtained. Operation control becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a fuzzy inference unit in FIG.

FIG. 3 is a diagram for explaining an inference method in a fuzzy inference unit.

FIG. 4 is a schematic configuration diagram of a power generation boiler.

[Explanation of symbols]

 1 Fuzzy inference part 2 Reference part 3 Correction part 4 Calculation part 1a Evaluation part 1b Rule part 1c Inference part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuichi Miyamoto 1-1 Kawasaki-cho, Akashi-shi, Hyogo Kawasaki Heavy Industries Ltd. Akashi factory (72) Inventor Eiichi Harada 1-1 Kawasaki-cho, Akashi-shi, Hyogo Kawasaki Heavy industry Co., Ltd. Akashi factory (56) Reference JP-A-3-29002 (JP, A)

Claims (2)

[Claims] 1. A coal combustion furnace of a pulverized coal combustion system in which coal is pulverized by a pulverized coal machine, only a pulverized coal having a predetermined particle size or less is separated by a coarse powder separator, and the separated pulverized coal is burned in a combustion furnace. In the above, the temperature in the combustion furnace, the load zone of the combustion furnace, the dirt factor of the combustion furnace, the ratio of the two-stage combustion air supplied to the combustion furnace and the mixed coal ratio of the coal supplied to the combustion furnace are fuzzy quantities. After taking in, inferring correction data and fuel ratio data for correcting the reference furnace temperature distribution, the reference furnace air ratio distribution, and the reference pulverized coal particle size distribution, which have been obtained in advance, and after inferring the correction data and the fuel ratio data. Each of the reference value of, and the ash unburnt content of the coal combustion furnace, characterized in that the ash unburned content concentration in the combustion exhaust gas is calculated based on the reaction rate ratio data of the coal obtained from the fuel ratio data Estimation apparatus. 2. A coal combustion furnace of a pulverized coal combustion system in which coal is pulverized by a pulverized coal machine, only a pulverized coal having a predetermined particle size or less is separated by a coarse powder separator, and the separated pulverized coal is burned in a combustion furnace. In, the temperature in the combustion furnace, the load zone of the combustion furnace, the dirt coefficient of the combustion furnace, the ratio of the two-stage combustion air to be supplied to the combustion furnace, and each data of the mixed coal ratio of coal to be supplied to the combustion furnace, Capture as fuzzy quantity,
A fuzzy inference unit for inferring correction data and fuel ratio data for correcting each reference value of the reference in-reactor temperature distribution, the in-reactor air ratio distribution, and the in-core pulverized coal particle size distribution that are obtained in advance, and the in-react furnace temperature Distribution, a reference part in which each reference value of the reference in-reactor air ratio distribution and the reference pulverized coal particle size distribution and the reaction rate ratio data of the coal for the fuel ratio data are stored, respectively, and the output from the reference part Based on the correction unit that corrects each reference value based on the correction data output from the fuzzy inference unit, based on the reference value corrected by the correction unit and the reaction speed ratio data output from the reference unit An ash-unburned-content estimating apparatus for a coal combustion furnace, comprising: a calculation unit that calculates the concentration of unburned-content in ash.